As a method for producing oxidation products of cycloalkanes, there has been known a method for oxidizing a cycloalkane with air by the catalysis of a transition metal compound such as a cobalt compound (see Japanese Unexamined Patent Application Publication (JP-A) No. H09-143109). This method, however, is disadvantageous in that the yield of a target oxidation product is generally low, and when the reaction is conducted for a prolonged time period in order to improve the conversion, the selectivity for the oxidation product is reduced. Additionally, the transition metal compound such as a cobalt compound, if contained in the product, may adversely affect typically a subsequent reaction or the properties of a downstream product, and this requires extra separation facilities for reliably removing such transition metal compound.
As a possible solution to these problems, there has been proposed a method for producing an oxidation product of a cycloalkane without using a cobalt compound, by oxidizing the cycloalkane in the presence of an imide compound having a cyclic imide skeleton (cyclic imide compound) (see JP-A No. 2003-128602). According to this method, an oxidation product of a cycloalkane can be produced with a high selectivity.
However, in the reaction using a cyclic imide compound as a catalyst in JP-A No. 2003-128602, the way to feed the cyclic imide compound to the reaction system is a problem, because the cyclic imide compound has a low solubility in the substrate. A major solution taken to this problem is dissolving the cyclic imide compound in an organic solvent. However, use of such an organic solvent is energetically disadvantageous, because this requires an extra operation, such as distillation, in a purification step so as to remove the organic solvent.
On the other hand, a reaction for converting a cycloalkyl hydroperoxide into a cycloalkanone and a cycloalkanol is one of industrially useful reactions and is used typically in a process of producing KA oil (a mixture of cyclohexanone and cyclohexanol) through oxidation of cyclohexane with oxygen. This reaction is generally carried out by mixing a liquid containing a cycloalkyl hydroperoxide with a transition metal catalyst, or an alkaline aqueous solution, or both, and a variety of techniques therefore have been reported.
JP-A No. H07-247230 discloses a method for producing an alkanone and/or an alkanol, by oxidizing an alkane and/or an alkene with oxygen to give an alkyl hydroperoxide and decomposing the alkyl hydroperoxide by the catalysis of a metallic compound catalyst such as a magnesium compound in the presence of a separated aqueous phase having a pH of more than 8.5, in which the catalyst is supported on a supporting material. JP-A No. H09-194408 discloses a method for producing a cycloalkanone and/or a cycloalkanol by decomposing a cycloalkyl hydroperoxide in the presence of an aqueous phase containing an alkali metal hydroxide and an alkali metal salt. JP-A No. 2004-59515 discloses a method for converting a cycloalkyl hydroperoxide into a cycloalkanone and a cycloalkanol by mixing a liquid containing the cycloalkyl hydroperoxide with a transition metal hydroxide and an alkaline (basic) aqueous solution. JP-A No. 2004-59541 discloses a method for converting a cycloalkyl hydroperoxide into a cycloalkanone and a cycloalkanol by mixing a liquid containing the cycloalkyl hydroperoxide with an N-hydroxy cyclic imide, a cobalt compound, and an alkaline aqueous solution.
Of cycloalkanones and cycloalkanols obtained by these methods, the cycloalkanols should be dehydrogenized so as to give cycloalkanones in many cases. Ultimately, high selectivity for cycloalkanones is desirable in decomposition reactions of cycloalkyl hydroperoxides. According to the above methods, however, the production ratios of cycloalkanones to cycloalkanols are low, and even when being high, at the best about 1.5. Additionally, according to the methods, cycloalkyl hydroperoxides are generally decomposed in the presence of a strong alkaline aqueous solution such as an aqueous sodium hydroxide solution so as to increase the decomposition rates of the cycloalkyl hydroperoxides. However, a strong alkaline aqueous solution such as an aqueous sodium hydroxide solution, if used in the reaction, causes undesirable oligomerization of cycloalkanones in a subsequent distillation step for separating the cycloalkanones and cycloalkanols, and to avoid this, there is a need of providing an extra neutralization step (Japanese Patent No. 3426213). This is a cause of increasing the production cost of cycloalkanones and cycloalkanols.
[Patent Document 1] JP-A No. H09-143109
[Patent Document 2] JP-A No. 2003-128602
[Patent Document 3] JP-A No. H07-247230
[Patent Document 4] JP-A No. H09-194408
[Patent Document 5] JP-A No. 2004-59515
[Patent Document 6] JP-A No. 2004-59541
[Patent Document 7] Japanese Patent No. 3426213